In U.S. Pat. No. 3,866,052, commonly-assigned herewith, the spatial locations of object surface points are determined by direct irradiation of a surface in a practice wherein segments of a projection field inclusive of the surface are selectively irradiated and a record made of the irradiated surface. In its principal practice, the U.S. Pat. No. 3,866,052 provides for subdividing the projection field and for successively projecting light into the subdivisions with individual photographs being made through a common fixed lens on each light projection. The line of sight between the lens node and the photographic representation of a surface point identifies a spatial line which extends to the actual surface point. The plane, with which such spatial line intersects to spatially locate the point, is identified by the selective presence or absence of a photographic representation of the point in the entire series of photographs. The spatial location of the lens node, if unknown, may be derived photographically by the use of discernible indicia in known spatial locations and reticle structure defining a reference surface with which the indicia are photographed as disclosed in U.S. Pat. No. 3,936,649, also commonly-assigned herewith.
In practice of the U.S. Pat. No. 3,866,052 method, object surface character is of significance. Thus, while surface reflectivity is required in order to obtain images of surface points in the photographs, various surfaces have reflectance characteristics which are specular or near-specular, and accordingly do not lend themselves to ready spatial location analysis by the U.S. Pat. No. 3,866,052 practice. Specular reflection is one in which a beam of light appears, after reflection, to proceed from an image of the light source existing in the reflecting surface, e.g., a mirror.